I used some Battery Monitor app (can't recall the name) that shows net battery use over time as a + or -. I tested quite a lot of situations including WiFi tethering. Yes, charging with regular USB while tethering with WiFI is a net loss to the battery. The USB input only slows the depletion. I was getting 14-18 hours out of my Bionic, so I was not among the 5-6 hours crowd at all, but when tethering, I was drawing enough mA's to drain a full battery in less than 3 hours. I collected data over a few days and found some interesting power draw patterns that don't jive with prior Android phone rules-of-thumb.
BTW - You want more amps not more voltage. Using the same monitoring mentioned above, I used a Nook charger capable of delivering .9 amps and the Bionic took every one of them. Charged from dead to full in under 2 hours.